1. Field of the Invention
The present invention relates to a heat treatment method which heats a substrate such as a semiconductor wafer including a high dielectric constant film formed on a silicon-germanium layer to promote the crystallization of the high dielectric constant film.
2. Description of the Background Art
Hitherto, silicon dioxide (SiO2) has been typically used as the material of a gate insulator film for a field-effect transistor (FET). However, as gate insulator films are made thinner with the decreasing size of devices, the increase in leakage current has become a problem. To solve the problem, a metal gate electrode such that metal is used as the material of a gate electrode has been developed while a material (a high dielectric constant material) having a dielectric constant higher than that of silicon dioxide is used as the material of a gate insulator film, as disclosed in U.S. Patent Application Publication No. 2011/0081753.
For the use of the high dielectric constant film (high-k film) made of such a high dielectric constant material, it has been studied to form a silicon-germanium layer having different concentrations to apply stresses to a source and a drain, thereby causing more current to flow.
However, a problem to be described below arises during the heat treatment of a semiconductor wafer in which a high dielectric constant film is formed on a silicon-germanium layer. The high dielectric constant film is formed by depositing a high dielectric constant material, using a MOCVD (metal organic chemical vapor deposition) technique and the like. The high dielectric constant film just deposited is low in crystallinity. It is hence necessary to anneal the high dielectric constant film at 1000° C. or higher, thereby promoting the crystallization of the high dielectric constant film.
However, heating of the silicon-germanium layer serving as a base layer to 1000° C. or higher alleviates the distortion between portions of silicon-germanium with different concentrations to result in a problem such that the capability of applying stresses to the source and the drain is decreased.